Are you new to MPS? Do you want to get an introduction into how languages are created? Then try this screen-cast. We'll walk through a robot-commanding sample DSL, introduce the individual aspects of its definition and see how they all fit together. Since the sample DSL is freely available in the MPS distribution, you'll be able to try it all out yourself.
If you're thinking of designing your own DSL or improving an existing language and want to get a feel for how MPS does these things, this screen-cast is for you.
If you haven't watched the first screen-cast of this series, you should probably check it out soon. It describes MPS from the developer's perspective and shows the robotcommanding DSL in action.
Note: The screen-cast features MPS 3.0 and is also applicable to a great extend to MPS 2.5.4.